Traveling-wave tube assembly



May 3,

J. J. CALDWELL, JR

TRAVELING-WAVE TUBE ASSEMBLY Filed oci. 7, 195?- fg W.

UnitedStates Patent Hughes Aircraft Company, Culver City, Calif., acorporation of Delaware Application october 7, 1957, seria1N0.6ss,704 6claims. (ctms-as) `This invention relates generally to electrondischarge devices and particularly to an improved traveling-wave tubewhich may be readily dismantled and re-assembled. Traveling-Wave tubesnormally comprise a numberr of major components such as one or moreelectron guns, a slow-wave structure and an electron collector, atransmission line coupling means and an envelope enclosing andsupporting these components. Usually these component parts aremanufactured as sub-assemblies and then -joined to the envelope by apermanent hermetic seal. Av serious problem relating to the iinalassembly of these component parts is the satisfactory provision of avery critical alignment of the electron gun and slow-wave structure.These' parts in turn must be precisely aligned with an external focusingmagnet in order to assure that the electron streamreaches the collectorelectrode Without impinging upon `the slow-wave structure. Suchimpingement of the electron Vstream would cause a serious deteriorationin tube performance and would inra very short period destroy a slow-wavestructure. Therefore, when such travelingwave tubes are initiallymanufactured they are` aligned very carefully and ordinarilypermanentlysealed together. In the normal operation of a traveling-wave tube, theend of the tubes life is often due to loss of athodeemission, burn-outof heater, gas evolution, Vor breakage due v,to accident or mishandling.This usually would require the actual replacement of only one minorelement. How-l over, because of the serious problem of `realigning thetraveling-Wave tube once it has been taken apart, it normally has beenthe practice in the past t discard the entire tube, including the:expensive slowawave structure, wave-guide couplings, and the anodeYelements of the lelectron gun. Heretofore, attempts to avoida permanentseal have been made without practical succe ss kA typical technique, forexample, has been toattach hcavyend pieces, separately supporting the'electron gun and the slow-wave structure, to the envelope. This method,h owever, has for the most part proved unsatisfactory, both in that thehermetic lseal is imperfect and in that additional weight is therebyadded tothe tube, making it less practical and mobile for airborneapplications.

y It is, therefore, an object of the present invention'to provide animproved electron tube which may readily and 4practicably bedismantledand ifo-assembled. Y

It is another object o f the present invention vto, provide atraveling-wave tube having an assembly of structure such that internalcomponents subject to deterioration with age may be "easily replacedWithout'discarding the entire tube.

It is a further object of the `present-invention tofprovide acomparatively lightweight traveling-wave vtube which may be dismantledfor -maintenanc'e'and inspectionpurposes without discarding the tubeland without requiring extensive skilled labor.

change of internal components may beiconverteda's `dic l ice tated bycurrent demands from one type of tube to another.

In one example of the present invention these and other objects areachieved by providing an outer aligning envelope and, at each end, anarrangement including aligning shoulders and an extended sealing lipmeans. The electron gun may be plugged into `one end and, once inserted,is automatically precisely aligned axially with the aligning envelope.Similarly, the slow-wave structure assembly, which includes input andoutput waveguide sections as well as the collector electrode, isinserted into the opposite end; Once inserted, the slow-wave structureis also automatically precisely aligned co-axially with the axis of theouter aligning envelope. In one embodiment, the end of the slow-wavestructure inserted furthermost into the aligning envelope is held inaxial alignment by additional aligning surfaces which are in fixedrelation to the aligning envelope. Once the two main sub-assemblies areinserted into the aligning envelope, all three ymembers areautomatically precisely aligned, Both the electron gun and the slow-wavestructure assembly are also provided with a peripheral sealing lipmatching with an associated lip ofv the aligning envelope. A vacuum seali's then provided by a peripheral sealing, as by a light weld, along theperiphery of the matching sealing lips at each end of the Aaligningenvelope. The tube may then by conyentionel means be degassed andevacuated.

The 'sealing lips are made slightly extended in a ner to provide anamount of expendable metal. By this arrangement the tube may bedisassembled and then rassembled. For example, the electron gun may berernoved by removing the peripheral weld about the sealing lips andsimply unplugging that subassembly. The'amount of heat required for thelight weld is suiciently small as to not destroy or an vany way affectthe laligning surfaces and retentive shoulders so that a repaired orreplacement electron gun may be readily reinserted and resealed byanother light peripheral weld.

The novel features which are believed to be characteristic of theinvention, both as to its organization Iand method of operation,together with further objects and advantages thereof, will be betterunderstood from Ythe following description considered in connection withthe accompanying drawing, in which like reference numerals refer tolikeparts and in which:

Fig. l is ay longitudinal sectional side view of a travelingwave tube inaccordance with the invention; and

Fig.` 2 is a longitudinal sectional side View, somewhat simplied, of asecond traveling-wave tube in accordance with theinvention.

A -In accordance with the invention, referring now to Fig. l, ademountable structure may be provided for us'ewith anv electron tube,such as a traveling-wave tube 10. Ai'- rangedwith the traveling-wavetube ltl'are the principal `operating units, including the collector 12,the electron gun 14, input and output waveguides 1'6 and 17 and aslow-wave structure 18. It will be understood the -details of thetraveling-wave tube lil have been Vsimplified for clarity and that thedrawing is not to scale.

The traveling-Wave 10 is provided with acylindrical aligning envelope orhousing 20 having a collector enjd'at the lefthand side (as viewed inthefigure) and an electron Vgun endvat the righthand side (also as viewedin VYthe figure). The cylindrical aligning envelope 20 includes, at thecollector end, an inner alignment shoulder y22. The 4envelope 20is/concentric with the longitudinal -axis of the traveling-wave tube 10vand the inner alignment shoulder 22 `is in a plane transverseto thislongitudinal axis. The aligning envelope 2li includes athin-walled'sealing ring-'24 at the extreme *lefthand or collector end.The 'relationship betwenuthe inner diameter' ofthe envelope VV20v-landcumference. l registers slidably with the inner surface of the sealingring the greater inner diameter of the sealing ringl 24 thus defines theinner alignment shoulder 22. The thin-walled sealing ring 24 may be, asshown, a part of the umtary cylindrical envelope 28, or it may beseparate from but affixed to the aligning envelope 20. The innercircumference of the thin-walled sealing ring 24 defines an allgnmentsurface for elements of the traveling-Wave tube 10 which are to beinserted and held in that end.

At the electron gun end of the cylindrical envelope 20 is a collarmember 38. The collar 30 lies substantially transverse to thelongitudinal axis of the tube 10 and is hermetically afiixed to therighthand end of the envelope 20. The collar 30 defines an inneraligning aperture 32 about the path of the electron stream in thetraveling-wave tube 10. The collar 30 includes an end ring 34 integraltherewith. The end ling 34 is concentric with the longitudinal axis ofthe traveling-wave tube 10 and includes an outer alignment shoulder 36and an outer alignment surface. The collar 30 also includes a thinsealing flange 40 extended outwardly from the collar 30. Together withthe outer alignment surface, the sealing flange 40 defines the outeralignment shoulder 36.

A transverse plate, hereafter called the collector end plate f), ismounted across the lefthand end of the cylmdrical aligning envelope 2G.The outer circumference of the collector end plate 56 is in engagementwlth the inner alignment shoulder 22 of the envelope 20. A thln-walledsealing ring 52 for the end plate 50 is concentric with the longitudinalaxis of the traveling-wave tube and is aflxed to the end plate 58 atrelieved portions of its cir- The outer surface of the sealing ring 5224 of the cylindrical aligning envelope 20 and assumes a positiondefined by the alignment surface on the thinwalled sealing ring 24. Thetwo sealing rings 24, 52 may be chosen to be coextensive for any desiredlength along the longitudinal axis of the tube 10, for purposes to bedescribed below. It is to be noticed, however, that the alignmentsurface on the sealing ring 24 and the inner alignment shoulder 22 ofthe cylindrical envelope 20 precisely define the position of thecollector end plate 50 when inserted in the collector end of thecylindrical aligning envelope 20. Therefore, the input and outputwaveguides, 16 and 17 respectively, and the slow-wave structure 18,which are mounted in appropriate receiving apertures in the collectorend plate 50, are likewise precisely positioned. It will be understoodthat the collector end plate 50 may be appropriately arranged to receiveand retain the principal traveling-Wave tube 10 structures, includingthe collector 12, the input and output waveguides 16 and 17 and theslow-wave structure 18. Additionally, the collector end plate 50 mayalso be employed to hold an exhausting tube (not shown) for evacuatingthe envelope 20.

Note also that when the slow-wave structure 18 is fully inserted, thefurthest inserted end registers with the edges of the inner aligningaperture 32 of the collar 30. The slow-Wave structure 18 may have ahub-like end 19, as

shown, -to engage the collar 30 for accurate seating and positioning bythe inner aligning aperture 32.

The matching lips which are thus defined by the thin- Walled sealingring 24 and the sealing ring 52 of the collector end plate S0 may bejoined together, as by a first light welding bead 60. This first lightwelding bead 60 provides an effective hermatic seal for the collectorend region of the traveling-wave tube 10. Heliarc welding is apreferable process for making the light welding beads without undue heatbeing applied to the component parts being welded.

At the electron gun end of the traveling-wave tube 10 is mounted anelectron gun support assembly 70. The electron gun support assembly 7 tlis in a general manner concentric about the longitudinal axis of thetravelingwave tube 10, and includes an outer tube structure 72 and aninner tube structure 74 axed and hermetically sealed thereto. The innertube structure 74 is employed for supporting the electron gun 14,including the cathode, filament, getter, connectors and other structuresusually associated therewith. The aligning portion of the electron gunsupport assembly 70 includes an annulus 76 fixed to the outer tubestructure 72. The inner circumference of the annulus 76 registersslidably with the outer alignment surface of the collar 30. The fittingbetween the inner circumference of the annulus 76 and the outeralignment surface adjacent the alignment shoulder 36 is such as topermit the support assembly 7l) to be slidably mounted on, but to beprecisely positioned by, the collar 30. The annulus 76 terminates on theside closest to the envelope 20 in a base flange 78 which registers withthe outer alignment shoulder 36 of the collar 30. The base flange 78 isin engagement with the outer thin sealing flange 40 of the collar 30.The radial length, from the center of the traveling-wave tube 10, overwhich the base flange 78 and the thin sealing fiange 40 are coextensivemay be varied as desired. It is, however, desirable to providesufficient material in this direction for several successive welds, asis described in detail below. A second light welding bead S0 joins thematching lips of the base fiange 78 of the electron gun and assembly 70and the thin sealing flange 40 of the collar 30. The second lightwelding bead 80, there fore, provides a hermetic seal at the electrongun end of the traveling-wave tube 10.

The structure shown in Fig. l is of an assembled traveling-wave tube 10.It is desired that the principal operating parts in this structure(slow-wave structure 18, collector 12, electron gun 14, etc.) beextremely precisely aligned. Such objectives are in fact met by thealignment relationships and structures provided.

At the collector end, for example, the entire structure supported in thecollector end plate 50 is mounted within the apertures in the end plate50 and may be inserted into the aligning envelope 20 as one unit. Thesealing ring 52 on the end plate 50 fits within the sealing -ring 24 ofthe aligning envelope 20, the limit of insertion of the end plate 50being precisely established by the inner alignment shoulder 22 of thealigning envelope 20. Movement of the end plate 50 normal to thelongitudinal axis of the tube 10 is prevented by the registeringsurfaces of the sealing rings 24, 52. Thus, the collector end plate 50and the attached collar, input and output waveguides 16 and 17 and theslow-wave structure 18 are precisely aligned with respect to each otherand the envelope 20. Further, the hub 19 on the furthest inserted end ofthe slow-wave structure 18 registers with the inner aligning aperture 32in the inner collar 30. Thus, the slow-wave structure 18 is additionallyrestrained frorn movement. Such restriction is often desirable becauseof appreciable forces acting upon such slow-wave structures 18.

The electron gun 14 is similarly precisely aligned with respect to thelongitudinal axis of the traveling-wave tube 10. The support assembly 70is arranged to hold the electron gun 14 in a fixed relation with respectto the annulus 76and the base flange 78 of the support assembly 70.Therefore, when the annulus 76 is fitted over the alignment surface onthe end ring 34 of the collar 30, the electron gun 14 assumes definiterelationships along and concentric with the longitudinal axis of thetube 10. Movement of the assembly 70 and the electron gun 14 parallel tothe longitudinal axis is limited by the engagement of the base flange 78with the outer alignment shoulder 36 of the collar 30. Thus, it may beseen that all the principal operating parts have precise relationshipswith respect to each other and to the longitudinal axis of the tube 10,through the use of the aligning envelope 20 and the attendant structure.

Further features of this invention provide the extremely valuablecapability of dismantling and 17e-assembling the tube 10. The firstlight welding bead 60 at the collector end vand the second light weldingbead 80 at the electron end maybelremovedras by a' grinding, cutting orm process. With the: lightwelding beads en, Si) ernployed and' with therelativclythin-walled sealing rings 224 52 or ilanges 40, 78 employed,the heat generated in this removal process is not sulicient to distortor other wise affect the remaining members of the traveling-wavetnbestrcture. After such disposal of the Welding beads 80',A therefore,either or both of the end assemblies maybe removedfrom the aligningenvelop to enable work to be performed on the parts involved.Thereafter, the Ypartmay` be reinserted in the same precise alignmentoi'ginally maintained. The tube may then be re-evacuated and anotherwelding bead 60 or 80 applied to the previously removed. The value ofhaving a coexive length of material available for subsequent rels andwelds Lwill now be apparent. For example, a derable length of materialmaybe provided at the s' lin rings 24, SZat the collector end if it isdesired to expriment with a@ number of different types of slowwavestructures 18, or to recheck thesame slow-wave structure 1S a number oftimesr In either event, the may be readily disassembled and the internalparts handled without requiring skilled labor, extensive measurementsoranentirely new structure.

'I "h'e, arrangement in Fig. 2 is a second exempliication oftheinvention which may be employed if desired. In Fig.2, s'ome parts likethose shown in l-lig. l are illustrated in simplified form for clarity.The basic arrangern nt of the collector 12 of the electron gun 14, theinput 'i utput waveguide 16 and 17 and the slow-wave structure18 is likethat shown in Fig. 1. The arrangement of th collector end plate 50 andthe rings 24, 52 at the to r end is like'that shown in Fig. l and thedescripwill not be repeated in detail here. In this arrangent, however,the aligning envelope 20 and the electron nd are disposed in a dilerentcombination. The aligning envelope, as shown in Fig. 2, may consistof aeqllector end half 2,0 and an electron gun half 20" which are afiixed`togetherat the center of the tube 10. Instead of the collar 30 of Fig. lthere is a collar 31 entirelywithin the envelope halves 20 and 20". Thiscol- 31 includes an inner aligning aperture 32 used with the h ub `19 ofthe slow-Wave structure 1S in the same manner as that shown in Fig. l.

Alignment of the electron gun structure 14 with respeet to the outeraligning envelope 20 is achieved by the use of an electron gun end plate71 and an electron sealing ring 73 in conjunction with a sealing ring 25atfthe extremity of the electron gun half 20 of the envelope., VThematching lips of the sealingrings 25, '73

arejoined by a light Welding bead 81.

The arrangement at the electron gun end may be seen to be similar tothat at the collector end, and a detailed de ription will not be given.T he traveling-wave tube byremoval of either orboth the end ringsections 24, 52 er 25, 7?, and precisely re-assembled with new orchanged structures. Thematching lips on the ring combinationsevacuation.

ltisftobe notedthat in both Fig. l and Fig. 2 the arrangement of theentire structure is such that all operng may b e dismantled.` Forexample, the input d output waveguides 16 and 17 respectively both exlilbfFig'. 2 may be dismantaled and precisely re-aligned thereafter againbe hermetically sealed after relfromthe collector end of the structure,so that no eacli end and" dii'erent" members each mating with adifferent one ofy the end rings. The terminal portions of the ringCombinations may be joined together to provide a hermetic seal. Therings are of sufficient length, however-,to permit the joined segmentsto be removed. Therebythe tube may be dismantled for repair orinterchanging of parts. The ring combinations are of suflicient lengthto provide a surplus of material which will permitre-fusing of the thenremaining terminal portions ofthe'se rings. This feature provides a tubewhich is practically adaptable to tube maintenance; which is ofcomparative light weight; and which may be rebuilt to serve as aYhigh-powered tube, a backward-wave oscillator, or an amplifier, byreplacement of internal comrenews.

What is claimed is:

H1 A rebuild-able traveling-wave tube housing comprisin'g: a hollowcylindrical member having a main body portion; a first sealing ring ofgreater inner diameter than the inner diameter of said main body portionand concentric therewith, said first sealing ring being fxedly coupledto one end of said main body portion and dening therewith an innercircumferential alignment shoulder; anV end plate abutting against saidinner circum- 'ferential alignment shoulder; a second sealing ringcoupled to said end plate in registry with the inner circumferenceofsaid rst sealing ring, said sealing rings being coextensive in thedirection of the longitudinal axis vof said cylindrical member; meanshermetically joining theterminal portions of said sealing rings; collarmeans xedly coupled to a second end of said main body portion, saidcollar means including an axially extending outer circumferentialalignment ring concentric with said cylindrical member and a radiallyextending circumferential sealing ange normal thereto and providingtherewith an outer circumferential alignment shoulder; a supportassembly closing the second end of said main bodyportion, said supportassembly including an annulus concentric with said main body portion andin registry with the alignmentring of said collar, said annulusterminatingin a circumferential ange abutting against sealin g flangesof said collar, said flanges being coextensive for a predeterminedlength in a direction normal to the longitudinal axis of saidcylindrical member; and means hermetically joining the terminal portionsof said anges.

2, An electron tube and housing comprising: a travelling-wave tube, anelongated slow-wave structure, an elongated cylindrical member disposedcoaxially with said slow-wave structure and having at least one end ringintegral with an end of said cylindrical member, said end ring having anouter diameter substantially equal to that of saidcylindrical memberandhaving a greater inner diameter than the inner diameter of theremainder of said cylindrical member thereby to provide an inneralignment shoulder at the juncture between said end ringjand saidcylindrical member, a ring member positioned withinsaid end ring, saidring member having substantially the same length as said end ring andbei ing concentric Withand engaging said end ring, a circucylindricalmember about said operative elements near` theirl end opposite said basemember to maintain in reproducible manner said operative elementsautomatically Vin accurate, predetermined relationship with saidelongated cylindrical member, and removable, rebuildable means sealingthe terminal portion of said end ring to the terminal portionof saidring member, whereby the ring )member may Vbe removed from said end ringby removinguthefsealed portion of said end ring and said ring member andwhereby said ring member may be re-sealed to said end ring by sealingthe then remaining terminal portions of said end ring to the thenremaining-terminal portions of said ring member.

3. A rebuildable traveling-wave tube comprising: a collector, anelongated slow-wave structure, an electron gun, an input waveguide, anoutput waveguide, a cylindrical housing enclosing said collector,slow-wave structure and electron gun, said housing comprising: a hollowelongated cylindrical member, rst and second circumferential meanscoupled to said cylindrical member at the different ends thereof andeach defining an axial reference shoulder and a circumferentialalignment surface, a collector ring member concentric with and disposedin a first end of said elongated cylindrical member, said ring memberincluding a collector end plate member secured thereto and engaging thereference shoulder associated therewith yfor supporting said collectorVand said elongated slow-wave structure, thereby to align the collectorand slow-wave structure with the cylindrical housing, collar meansconcentrically supported within said cylindrical housing for removablyand rebuildably supporting said slow-wave structure in axial alignmentwith said cylinder housing, an electron gun ring member concentric withand disposed in the second end of said elongated cylindrical member,said electron gun ring member having an electron gun ring end platesecured to said ring member and in contact with the reference shoulderassociated therewith, means sealing the terminal portions of saidcollector ring member and said electron gun ring member to theirrespective ends of said hollow elongated cylindrical member, wherebysaid traveling-wave tube may be dismantled and rebuilt by removing andresealing the sealed terminal portions.

4. A rebuildable traveling-wave tube comprising: an electron gun, acollector, a slow-wave structure positioned intermediate said electrongun and said collector with one end of said slow-wave structure securedto said collector, a hollow elongated cylindrical member disposed aboutsaid slow-wave structure and portions of the electron gun and thecollector and having rst and second end rings integral with the mainbody portion and disposed on opposite ends thereof and being of greaterinner diameter than the inner diameter of the adjacent main body portionthereby to provide iirst and second inner alignment shoulders at thejunctures between said end rings and the endsV of said main bodyportion, an electron gun ring member positioned within said iirst endring and concentric therewith, and registering with the inner Walls ofsaid tirst end ring, said electron gun ring member also including anelectron gun end plate engaging said first alignment shoulder thereby toalign an electron gun sup- 'ported by said electron gun end plate alongthe axis of 'the traveling-wave tube and also with the main body portionof said hollow elongated member, a collector ring member positionedwithin said second end ring and concentric therewith and registeringwith the inner walls of said second end ring, said collector ring memberincluding a collector end plate secured to said collector ring memberand engaging said second alignment shoulder thereby to align a collectorsupported by said collector end plate with the electron gun, saidcollector base member having a collector aperture, an input waveguideaperture and an output waveguide aperture, first and second meanswelding the terminal portions of said electron gun ring member and saidcollector ring member to the terminal portions of said rst and secondend rings respectively, an internal collar having a central aperture andengaging the inner surface of the main body portion of said hollowelongated member, said collar being positioned intermediate theslow-wave structure and the electron gun and receiving, at the aperturethereof, a portion of the slow-wave structure, and input and outputwaveguides passing through their respective apertures in the collectorbase member for introducing and extracting an electromagnetic signalfrom the slow-wave structure, whereby the welded portions of saidterminal portions of said iirst and second end rings and said electrongun and collector ring members may be removed for internal' maintenanceof the traveling-wave tube and whereby the then remaining portions ofsaid terminal portion of said first and second end rings and saidelectron gun and collector ring members may be rewelded.

5. A rebuildable traveling-wave tube comprising: an electron gun; acollector; a slow-wave structure positioned intermediate said electrongun and said collector; input and output waveguides coupled to saidslow-wave structure and extending past said collector; a cylindricalenvelope disposed about said slow-wave structure, said envelopeincluding a relatively thin collector end ring integral with the mainbody portion of said envelope and disposed at the collector end thereof,said collector end ring being of greater inner diameter than theadjacent diameter of the main body portion, thereby to provide an inneralignment and an inner aligment shoulder at said collector end; acollector base end plate hermetically retaining said collector,slow-wavc structure and waveguides and positioned within said collectorend ring transverse to the longitudinal axis of said envelope, said endplate abutting against the alignment shoulder of said envelope; a`collector sealing end ring coupled to said collector end plate andconcentric therewith, said collector end ring registering at its outercircumference with the inner circumference of the alignment surface onthe end ring portion of said envelope, thereby to provide a coextensivesealing portion along the longitudinal axis of said envelope; a collarhaving a central aligning aperture for receiving a portion of saidslow-wave structure, said collar being mounted transverse to saidenvelope at the electron gun end thereof, said collar including a ringportion defining an outer alignment surface concentric with saidenvelope and a relatively thin sealing flange normal to the longitudinalaxis of said envelope and dening an alignment shoulder with thealignment surface of the ring of said collar; an electron gun supportassembly, including coupled outer and internal tubes for supporting saidelectron gun, said electron gun support assembly including at the saidouter tube an annulus concentric with said envelope, the innercircumference of said annulus registering with the outer alignmentsurface defined by the ring of said collar, said electron gun supportassembly being terminated in a relatively thin circumferential base angein engagement with said sealing flange portion of said collar, said baseange and said sealing ange being coextensive for a predetermined radiusin a direction normal to the longitudinal axis of said envelope; andwelding beads joining and sealing the matching lips defined by theterminations of the registering sealing rings at the collector end andthe terminations of the registering sealing' anges at the electron gunend.

6. An electron tube and housing comprising: a traveling-wave tube, anelongated slow-wave structure, an elongated cylindrical member disposedcoaxially with said slow-wave structure and having at least one end ringintegral with -a first end of said cylindrical member, said end ringhaving an outer diameter substantiallyequal to that of said cylindricalmember and having a greater inner diameter than the inner diameter ofthe main body portion of said cylindrical member thereby to provide aninner alignment shoulder at the juncture between said end ring and saidcylindrical member, a ring member positioned within said end ring, saidring member having substantially the same length as said end ring andbeing concentric with and engaging said end ring, a circular base membersupporting elongated, operative elements of said travelingwave tube andsecured to an end of said ring member and engaging said alignmentshoulder, concentric'collar means supported within said cylindricalmember about said operative elements near their end opposite said basemember to maintain in reproducible manner said operative elementsautomatically in accurate, predetermined relationship with saidelongated cylindrical member, re-

movable, rebuildable means sealing the terminal portion of said end ringto the terminal portion of said ring member, whereby the ring member maybe removed from said end ring by removing the sealed portion of said endring and said ring member and whereby said ring member may be re-sealedto said end ring by sealing the then remaining terminal portions of saidend ring to the then remaining terminal portions of said ring member,and second removable, rebuildable means at the second end of saidcylindrical member for supporting others of said operative elements inaccurate axial alignment with said cylindrical member, said second meansincluding a pair of relatively thin terminally removably and rebuildablyf 10 joined peripheral members which are at least partially coextensiveand in engagement and which when rebuild- .ably joined reproduce saidaccurate axial alignment.

References Cited in the iile of this patent UNITED STATES PATENTS2,402,020 Dorris June 11, 1946 2,509,649 Norman May 30, 1950 2,708,727Quate May 17, 1955 2,727,179 Lally et al Dec. 13, 1955 2,788,465 Bryantet al. Apr. 9, 1957 2,822,492 Burke Feb. 4, 1958 UNTTED STATES PATENTOFFICE CERTIFICATE OFy CORRECTIUN Patent No. 2,935,641

Joseph J. Caldwell, Jr.

May 3, 1960 It is hereby certified that error appears in the-printedspecification of the above numbered patent requiring correction and thatthe said Letters Patent should read as corrected below.

Column 3 line 65, for "hermaticl read hermetic oolulmm 5, line 55, for"dismantaled," read ollsmentled column 7, line 22, for "cylinder" readcylindrical Signed and sealed this 11th day of October 1960,.d

(SEAL)' Attest: KARL H. AXLINE ROBERT C. WATSON Attestin 4OfficerCommissioner of Patents

